1. Field of the Invention
The present invention relates to a piezoelectric tuning fork resonator and a method of manufacturing the same.
2. Description of the Background Art
As a piezoelectric tuning fork resonance component, comprising sealing substrates which are hardly split or cracked, and a vibrating part which is excellent in airtightness/sealability, the inventor has proposed a piezoelectric tuning fork resonance component, which is improved in portions that are provided with terminal electrodes for being electrically connected with the exterior (Japanese Utility Model Application No. 3-73941 (1991)). The structure of this piezoelectric tuning fork resonance component has not yet been opened to the public.
FIGS. 2 and 3 are an exploded perspective view and a perspective view respectively, for illustrating such a piezoelectric tuning fork resonance component.
Referring to FIG. 2, a piezoelectric tuning fork resonator 1 comprises a piezoelectric substrate 2, which is in the form of a rectangular plate, and tuning fork grooves 2a to 2c, which are formed in the piezoelectric substrate 2 for defining a pair of tuning fork arm portions 3 and 4. In the vicinity of the innermost part of the tuning fork groove 2a, a resonance electrode 5 is formed on an upper surface of the piezoelectric substrate 2. This resonance electrode 5 is electrically connected to a lead electrode 6, which is formed on a position of the upper surface of the piezoelectric substrate 2 reaching an edge thereof. Numeral 7 denotes a dummy electrode.
On a lower surface of the piezoelectric substrate 2, another resonance electrode 8 is formed so as to be opposite to the resonance electrode 5 which is formed on the upper surface of the piezoelectric substrate 2, as shown in a downwardly projected manner. This resonance electrode 8 is electrically connected to a lead electrode 9, which is formed on the lower portion of the piezoelectric substrate 2 to reach an edge thereof. Numeral 10 denotes another dummy electrode.
A dummy substrate 11 is arranged on a side of the piezoelectric tuning fork resonator 1 with a clearance A defined between the dummy substrate 11 and the tuning fork arm portions 3 and 4. Dummy electrodes 12a and 12b are provided on an upper surface of the dummy substrate 11, while dummy electrodes 13a and 13b are provided on its lower surface, as shown in a downwardly projected manner. The dummy substrate 11, which is formed by a ceramic substrate having the same thickness as the piezoelectric substrate 2, which is arranged on its side, is provided with the dummy electrodes 12a, 12b, 13a and 13b in order to attain coincidence of the total thickness of the component.
The piezoelectric tuning fork resonator 1 is structured so as to function as a two-terminal piezoelectric vibrator upon application of alternating voltages to the lead electrodes 6 and 9.
Rectangular frame members 35 and 36, and sealing substrates 37 and 38 are stacked on upper and lower portions of the piezoelectric tuning fork resonator 1 and the dummy substrate 11, and pasted thereto with an insulating adhesive, thereby obtaining a laminate 14 shown in FIG. 3. Terminal electrodes 15 and 16, and dummy terminal electrodes 17 and 18 are provided on end surfaces of this laminate 14, thereby forming a piezoelectric tuning fork resonance component 19. The terminal electrodes 15 and 16 are formed so as to be electrically connected to the lead electrodes 6 and 9.
In this piezoelectric tuning fork resonance component, the terminal electrodes 15 and 16 provided on end surfaces of the laminate 14, as described above, whereby the sealing substrates 37 and 38 are hardly cracked or split in handling.
While a conventional piezoelectric tuning fork resonance component has notches, which are provided on edges of sealing substrates for extracting lead electrodes and electrically connecting the same with the exterior, the aforementioned piezoelectric tuning fork resonator, which has been proposed by the inventor, is provided with no such notches. Therefore, contact areas between the piezoelectric tuning fork resonator and the sealing substrates can be increased to attain improved airtightness/sealability of the vibrating part.
Even in such a structure, however, airtightness/sealability could be occasionally damaged. When the frame members 35 and 36 and the sealing substrates 37 and 38 are stacked on upper and lower portions of the piezoelectric tuning fork resonator 1 and the dummy substrate 11, and pasted thereto with adhesives, some adhesive generally flows into the clearance A between the dummy substrate 11 and the piezoelectric tuning fork resonator 1 to maintain airtightness in the interior. However, the piezoelectric tuning fork resonance component 19 may occasionally be produced without the adhesive completely flowing into the clearance A. In such a case, airtightness/sealability is not attained.
To this end, the inventor has further proposed a piezoelectric tuning fork resonance component, which has adhesive layers provided on both sides of the tuning fork arm portions, for integrating a piezoelectric tuning fork resonator with a dummy substrate by the adhesive layers while defining a clearance between the dummy substrate and the tuning fork arm portions (Japanese Patent Application No. 4-127591 (1992)). The structure of this piezoelectric tuning fork resonance component has not yet been opened to the public either. FIG. 4 is an exploded perspective view showing such a piezoelectric tuning fork resonance component. Referring to FIG. 4, adhesive layers 41 and 42 are provided on both sides of tuning fork arm portions 3 and 4 of a piezoelectric tuning fork resonator 1, for integrating the piezoelectric tuning fork resonator 1 with a dummy substrate 11. These adhesive layers 41 and 42 are formed so that a clearance A is defined between the piezoelectric tuning fork resonator 1 and the dummy substrate 11.
Thus, it is possible to seal the clearance A between the piezoelectric tuning fork resonator 1 and the dummy substrate 11 with the adhesive layers 41 and 42, thereby improving airtightness of the overall piezoelectric tuning fork resonance component.
In the aforementioned structure, which has been proposed by the inventor, it is necessary to provide the adhesive layers 41 and 42 so that the clearance A is defined between the piezoelectric tuning fork resonator 1 and the dummy substrate 11, so as not to hinder the tuning fork arm portions 3 and 4 of the piezoelectric tuning fork resonator 1 from vibration. However, since the adhesives for forming the adhesive layers 41 and 42 are generally in the form of liquids, the tuning fork resonator 1 could be excessively integrated with the dummy substrate 11. In this case, the clearance A between the dummy substrate 11 and the piezoelectric tuning fork resonator 1 could be reduced so that the tuning fork arm portions may be hindered from vibration.
On the other hand, a method of manufacturing such a piezoelectric tuning fork resonator has the following problem:
In a general step of forming tuning fork grooves in a piezoelectric substrate, a plurality of piezoelectric substrates are superposed so that edges thereof are aligned with each other, and tuning fork grooves are simultaneously formed in the edges of the plurality of piezoelectric substrates which are superposed with each other.
In such a conventional method, however, frequency accuracy of the obtained piezoelectric tuning fork resonator is merely about .+-.3% with respect to a set value. Thus, a piezoelectric tuning fork resonator cannot be obtained in high frequency accuracy. In such a piezoelectric tuning fork resonator, the frequency of a vibration mode is determined by depths of the tuning fork grooves, which in turn are determined by distances from the edges of the piezoelectric substrate. In the piezoelectric substrates which are superposed with each other, however, such edges are not may not be accurately aligned with each other, and hence the depths of the tuning fork grooves formed are dispersed in the respective piezoelectric substrates. Thus, it is impossible to attain high frequency accuracy.
In order to solve this problem, the tuning fork grooves may have to be formed in each piezoelectric substrate separately. In this case, however, productivity is extremely deteriorated.